In particular, the invention relates to a cleaning device that moves back and forth in a swimming pool, said cleaning device having a drive mechanism that can be switched to forward or backward travel and that is actively connected to drive wheels or drive tracks, with a motor being provided for each of a left-hand side and a right-hand side part of the drive mechanism, respectively. Also provided is a control apparatus to control the drive mechanism, and contact means arranged at the front and rear to generate control signals in the event that the cleaning device runs up to a swimming pool wall or an obstacle. In addition, the control apparatus includes a speed control unit for each part of the drive mechanism, i.e. for each of the two motors, and means to differentially control the speed of both motors. Furthermore, the cleaning device has means at both parts of the drive mechanism to measure the distances traversed during travel. An example of such a cleaning device has been disclosed in EP-0 989 256. Cleaning devices of this type can be used in swimming pools of a wide diversity of shapes since, due to their design and the working method implemented, they do not require a reference swimming pool wall for alignment.
Differential speed control to control the two motors during travel has been implemented in EP-0 989 256 such that they are operated at different constant rotation rates at least part of the time, which is to say during the changes in direction to be carried out, in order to thereby accomplish controlled angular changes in direction. In the process, the angular change in direction desired can be determined by the difference in rotation rates since the path traversed is measured at both parts of the drive mechanism, and thus the different arc lengths are known. Although ramp functions for speed development are provided for the start phases, the changes in direction are essentially done at the speed of travel used to clean the swimming pool.
However, it has been found that in swimming pool cleaning devices of this type, gradually increasing deviations from the direction of motion (path direction) originally established nevertheless very often occur. This can be the case for larger swimming pools in particular, for example 50-m pools, which require a large number of cleaning passes. Investigations have shown that each time the cleaning devices run up to an edge of the swimming pool or an obstacle, the jolt caused by abrupt braking or impact usually causes a backward displacement or a rotation, albeit only slightly. As the number of abrupt braking motions increases, these path errors accumulate. For the most part, mechanical devices continue to be used as contacting means since other sensors, such as those that are optics based, rapidly fail or provide unreliable results especially in turbid water. Frequently, it is additionally also the case that the deflection length of the mechanical switching element is too small relative to the required braking distance of the cleaning device, so that the offsets that occur upon impact are further amplified as a result of the inertia of the cleaning device.